The invention relates to a capped electric lamp comprising
a light-transmitting lamp vessel accommodating an electrical element,
a lamp cap provided with a projecting contact pin having an axis, which lamp cap is secured to the lamp vessel,
an electric conductor which is connected to the electrical element and to the contact pin,
an indentation being formed in the contact pin to fix the electric conductor.
The invention also relates to a low-pressure mercury vapor discharge lamp.
Such an electric lamp is disclosed in GB-A 0 692 290. In the known lamp, wedge-shaped indentations are situated on either side of the contact pin and opposite each other, which indentations are used to shrink the contact pin so as to contact the electric conductor.
The known capped electric lamp is a fluorescent lamp having two contact pins at the lamp cap. In a fluorescent lamp, mercury is the primary component for (efficiently) generating ultraviolet (UV) light. An inner wall of the discharge vessel may be coated with a luminescent layer comprising a luminescent material for converting UV to other wavelengths, for example to UV-B and UV-A for tanning purposes, or to visible radiation for general illumination purposes. The discharge vessel of said fluorescent lamps is generally tubular with a circular cross-section and includes both elongated and compact embodiments.
A drawback of the known capped electric lamp resides in that, during the manufacture of the lamp, more particularly when the contact pin is provided with the indentation, the end portion of the electric conductor projecting from the contact pin is subjected to a pulling force to preclude that the electric conductor in the lamp cap or in the lamp vessel electrically contacts a further electric conductor which has been passed through an adjacent contact pin. After fixing the electric conductor in the contact pin, said projecting end portion of the electric conductor must be removed. This is achieved by cutting and/or filing. This constitutes a drawback because additional safety measures must be taken to ensure that these operations are carried out in a safe and clean manner. In the case of the much used tubular fluorescent lamps comprising two such lamp caps, which are each provided with two contact pins, said drawback increases accordingly.
It is an object of the invention to provide a capped electric lamp of the type mentioned in the opening paragraph, wherein said drawback is obviated.
In accordance with the invention, this object is achieved in that the electric conductor in the contact pin does not extend beyond a boundary of the indentation that is furthest removed from the lamp cap.
The indentation in the contact pin is formed in the course of the manufacture of the electric lamp by an inward deformation of the contact pin. By locally indenting the contact pin, the electric conductor is fixed in the contact pin. As a result of said indentation, the electric conductor is weakened near the boundary of the indentation to such extent that, upon exerting a pulling force on the end portion of the electric conductor projecting from the contact pin, the electric conductor breaks off at a predetermined location. By providing the electric conductor with a predetermined weakened portion, the electric conductor breaks off near the boundary of the indentation. After breaking off the electric conductor, (the end portion of) the electric conductor no longer projects from the contact pin. As a result, cutting and/or filing of the end portion of the electric conductor projecting from the contact pin after fixing the electric conductor has become superfluous.
It is to be noted that the exertion of a pulling force on (the end portion of) the electric conductor can alternatively be carried out, after fixing the electric conductor in the contact pin, by suitably twisting the end portion of the electric conductor projecting from the contact pin. Experiments have further shown that upon pulling loose the end portion of the electric conductor, the fixation resulting from the indentation of the contact pin is sufficiently strong, so that the end portion of the electric conductor can be pulled loose independent of the fixation of the electric conductor.
Indenting the contact pin to weaken the electric conductor preferably takes place unilaterally. The indentation is generally formed in the contact pin by means of a so-called pinching pin, which is pressed against the contact pin in a direction transverse to the axis, causing the contact pin to be deformed in an inward direction.
A preferred embodiment of the capped electric lamp in accordance with the invention is characterized in that the indentation has a pinch portion near the boundary, which serves to weaken the electric conductor during the manufacture of the electric lamp. The term xe2x80x9cpinch portionxe2x80x9d is to be taken to mean in the description and the claims of the invention under consideration that, during the indentation process, the contact pin is locally pressed deeper into the electric conductor and at a more acute angle. This pinch portion does not xe2x80x9ccutxe2x80x9d the electric conductor but causes the electric conductor to be weakened such that upon exerting a pulling force on the end portion of the electric conductor, said electric conductor breaks off at a predetermined location. The use of such a pinch portion has the advantage that the electric conductor remains fixed in the contact pin during and after the removal of the projecting end portion of the electric conductor. Exerting a pulling force on the projecting end portion of the electric conductor, after indentation of the contact pin, does not cause the fixation of the electric conductor in the contact pin to be weakened such that the electric conductor is no longer fixed in the contact pin.
In a particularly preferred embodiment of the capped electric lamp in accordance with the invention, the pinch portion deepens in the direction of the front boundary at an angle ranging from 10xc2x0xe2x89xa6xcex1xe2x89xa645xc2x0, wherein the angle xcex1 is measured with respect to the axis. To fix the electric conductor, use is made of a so-called pinching pin. At an angle xcex1 less than 10xc2x0, the weakening of the electric conductor during the provision of the indentation is insufficient to cause the end portion of the electric conductor to become detached from the electric conductor when a pulling force is applied, while at the same time the electric conductor remains fixed in the contact pin. Furthermore, at an angle xcex1 less than 10xc2x0, the pulling force necessary to remove the end portion of the electric conductor is so large that the fixation of the electric conductor in the contact pin is annihilated almost completely. At an angle xcex1 greater than 45xc2x0, aging of the pinching pin occurs rapidly due to the fact that the pinch portion breaks off readily owing to too high a pressure on said pinch portion.
Preferably, the pinch portion deepens at an angle in the range from 25xc2x0xe2x89xa6xcex1xe2x89xa635xc2x0. Experiments have shown that the use of a pinching pin having such a pinch portion enables the end portion of the electric conductor to be removed while preserving the fixation.
The indentation 15 further comprises a press portion for fixing the electric conductor. The combination of the press portion and the pinch portion causes a synergetic effect to be obtained. On the one hand, the pinch portion weakens the electric conductor upon indenting the contact pin and, on the other hand, the press portion causes the electric conductor to be fixed in the contact pin such that the end portion of the electric conductor can be readily pulled loose without the fixation of the electric conductor being substantially reduced. To this end, the length of the press portion in the fixation area is preferably chosen to be such that upon pulling the end portion of the electric conductor from the contact pin, the electric conductor remains fixed in the contact pin.
It is particularly favorable if the contact pin 4 has only one indentation 15. This enables the pinch portion and the press portion to be provided in a single operation.
The measure in accordance with the invention can particularly suitably be applied to low-pressure mercury vapor discharge lamps comprising a capped electric lamp in accordance with the invention wherein the lamp vessel encloses a discharge space provided with a filling of mercury and an inert gas in a gastight manner, and wherein the electric element comprises an electrode arranged in the discharge space for maintaining a discharge in said discharge space.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter.